1. Field of the Invention
The invention pertains to the preparation of adhesive compounds intended to be sprayed on mineral fibers constituting fleeces or felts, especially for thermal and acoustic insulation. These compounds give the felts which are formed their cohesion and, in a more general manner, their mechanical properties. The compounds in question can vary quite appreciably depnding on the purpose of the felts, even when, as in the most common forms, the base resin for these compounds is still the amino plastic, phenolic plastic and especially formo-phenolic (amine modified or otherwise) type.
2. Background of the Prior Art
In addition to the resin, in general, the compound which is sprayed on the fibers thus traditionally comprises various ingredients which either improve the former's action or which add supplementary properties. In addition, it is known to add constituent in addition to the resin which also act as bonding agents. This is the case, for example, with carbamide or ammonium lignosulfonate. It is also customary to add an oil emulsion to the compound which acts as a softener and dust-proofer. Certain glass-resin "coupling" agents are also added, which facilitate the bonding of the resin to the fibers. These include amino-silanes, for example. Filler materials, coloring, waterproofing agents such as silicones, etc. are also added.
A catalyst must also be added for the cross linkage of the resin which will promote the subsequent processing. Of course, this constituent cannot be added very long before the adhesive is applied to the fibers when its nature is such that it initiates an evolution towards cross linkage under surrounding conditions. Finally, in addition to the fact that the resin can run the risk of premature transformation if produced in very large quantities and increase the time periods between production and consumption (taking into account the proportion of water needed and the volume these compounds reach), it is preferably for reasons of storage convenience not to prepare the adhesive until immediately before it is used.
For example, it is generally preferable to limit storage time to a few hours. For some compounds, this period does not exceed 24 hours but can be shorter for certain compounds, for example, about 1 hour, or even less.
Moreover, products prepared on the same production line can quite often vary. In the hypothesis in which each adhesive would be prepared independently of immediate consumption, access to a complete range of adhesives would be necessary. This becomes less desirable as the variety of adhesives utilized increases.
For these reasons, the adhesives are usually prepared gradually as they are consumed. The problem is to ensure continuous preparation under economically satisfactory conditions. It is especially necessary to reduce operator intervention as much as possible. The cost of the special equipment used must also remain compatible with the economic objective established for the adoption of these techniques. In other words, simple solutions are needed which require a small number of personnel and moderate-cost equipment, while of course maintaining the quality of the adhesives prepared.
The traditional preparation method consists of placing the various constituents together in a tank, the proportions of which are measured by an operator when they are added. Taking into account the need for operator control, the preparation operations tend to be spaced and relatively large quantities are involved for each of these preparations. These two factors constitute an obstacle against frequent changes of the type of adhesive and require large storage capacities.
More recently, it was attempted to automate the preparation sequences allowing them to occur more frequently and thus involve smaller quantities.
It was proposed to prepare the adhesive compounds by adding the different constituents of the mixture using dosing pumps set to add these constituents in the required proportions. Even if it was proposed to prepare the compound continuously, as a direct function of its consumption, the most widespread solutions consist of making successive small-volume lots, with a previously prepared lot being consumed while the subsequent lot is being prepared.
A problem with this preparation method is related to the fact that the dosing pumps used must be very precise. Volumetric piston pumps are especially used. This equipment requires frequent maintenance. The equipment is also relatively expensive.
Moreover, the use of these volumetric pumps involves problems with respect to their automatic adjustment. It is known to modify their flow rate by changing the piston cycle or by modifying the operating speed, for example, but each of these methods involves its own problems. Speed modification, which is done especially using speed variators, does not allow a great degree of precision to be maintained over long periods of use. To modify the piston cycle, the pump must be connected to complex electromechanical equipment. For these reasons, the adjustment of prior equipment is rarely automated and operator intervention is limited by avoiding frequent production changes. But this obviously does not respond perfectly to practical needs.
An object of the invention is to propose a method for the preparation of the adhesive compound which is both reliable and precise, a preparation which is done in small quantities for each operation.
Another object of the invention is to propose such a method of preparation in which the constituents are measured preferably with a number of measuring devices which is smaller than the number of constituents used.
Another object of the invention is to allow the quantities of constituents utilized to be controlled instantaneously and automatically in the method for the preparation of the adhesive involved.
Another object of the invention is to allow an assessment of available compound to be prepared simultaneously so as to adjust the amount of compound being prepared to the quantity of felt of a given quality remaining to be prepared in the production sequence in progress. This assessment can also be combined with that of each of the constituents in stock to facilitate the management thereof.
Another object of the invention is to propose an installation which makes it possible to greatly reduce operator intervention for the adjustment of maintenance thereof.